[ ♪ INTRO ] In recent years, scientists have used some  of the most precise astronomical tools ever developed to detect incredible and  extreme objects within our galaxy. ~ One of the latest, reported in 2021,  is a small but incredibly dense star that’s spinning on its axis  more than twice a minute.

It’s the fastest spinning star ever detected. What’s more, this wildly wheeling star also seems to be spraying stuff out into  space, just like a lawn sprinkler!

To try and understand why  it’s behaving so weirdly, scientists need to look deeper into how  this rare and exotic star came to be. Why is it spinning so fast, and where is all the stuff coming from? It’s worth mentioning that pretty  much everything in the universe spins.

Our own sun, for example, completes  a full rotation about once a month, and the Earth spins once a day… by definition. But the fastest-spinning stars  put both of these to shame. Astronomers use highly sensitive  instruments alongside powerful telescopes to detect faint pulses of  light from spinning stars.

Those pulses are thought to come from  bright spots on the stars’ surfaces, and so the speed of the pulses lets  us calculate the speed of rotation -- a bit like a sweeping lighthouse beam. Until recent times, there seemed to be only one of  these record-breaking spinners. Known as AE Aquarii, it was bright enough  to be seen in telescopes from the 1940s, and analysis in 1979 showed that it appeared  to be rotating once every 33.08 seconds.

That means it’s already spun around more than  twice while you’ve been watching this video! But in 2021, astronomers finally managed  to pinpoint the speed of another star, with the catchy name  J0240-1952, or J0240 for short. And it seems to be spinning even faster.

To pick up its faint pulsing signal, they used a high speed camera on  the huge Gran Telescopio Canarias, part of an observatory in the Canary Islands. J0240 completes a full  rotation every 24.9 seconds. That’s nearly 25% faster than AE Aquarii.

J0240 spins more than 93,000 times in the  time it takes for our Sun to rotate just once. But both AE Aquarii and J0240  are nothing like our sun. They’re actually white dwarfs.

These small, hot bodies are the cores left over  after the death of a typical main sequence star. These are stars like our Sun that fuse hydrogen i n their cores for many millions of  years, until their nuclear fuel runs out. So, instead of being sustained  by nuclear fusion, white dwarfs are so dense that the repulsion of electrons  in their core is what keeps them going.

White dwarfs have at least  half the mass of our Sun, but are packed into a sphere  about the size of the Earth. That gives them a density some 200  thousand times greater than the Earth, and correspondingly huge gravities  and strong magnetic fields. But the fastest spinners  in the galaxy aren’t alone.

Both AE Aquarii and J0240 are part of binary  systems with another, red giant star. ~ And it’s as these two stars interact  that things get really interesting. The intense gravity from the white dwarf  pulls material from its partner star, channeling it onto its own surface. Kind  of like a parasite feeding on its host.

Remember that the white dwarf has run out  of fuel, but it is still incredibly dense. So when fresh hydrogen fuel  is pulled onto its surface, the gravity is enough to compress  it and start off fusion again. But because this fuel is in the outer layer, the energy it generates is enough to blow away  the remaining unignited gas in a bright flash of light, traditionally known as a nova.

That process repeating over and over again  gives these kinds of stars a very cool name: cataclysmic variables! There are all kinds of  cataclysmic variables out there, and the precise dynamics of  accumulation and explosion   depends on the white dwarf’s magnetic field. If the field is weak, then the secondary  star’s gas forms an accretion disk around the white dwarf’s equator, and material gradually  rains down onto the surface.

If the magnetic field is really strong, then the two stars become locked in a dance, where their rotational  speed matches orbital speed, a bit like how the moon is  tidally locked to the Earth. ~ The material is then channeled in a single  stream toward the white dwarf’s poles. But if the magnetic field is somewhere in  between, not too strong and not too weak, then the red giant’s material ends up  spiralling around and getting tangled up. It occasionally falls to the  surface in quick spurts. ~ These spurts do still have some  spin from their initial spiral, so as they slap into the white dwarf’s surface,  they give it a little extra push around.

Repeated over and over again, this has the  effect of powering the white dwarf’s spin, just like spinning a carousel faster  and faster by pushing it every so often. With J0240, astronomers have even been able  to see the point where it’s being “pushed”, as a spot covering about 2% of the surface  that’s unbelievably hot, at about 30,000 Kelvins. Now, we think this star has been spun up about as  fast as it can go without completely flying apart.

But the strong magnetic fields  here are also having another, unexpected effect on the  incoming stellar material. Not all of the gas makes it to  the surface of the white dwarf. The star’s incredibly fast spin  and powerful magnetic fields are enough to eject some of the  channeled gas back out into space.

The result is blobs of gas being  sprayed out all around the white dwarf, just like a rotary lawn sprinkler! The phenomenon is called a magnetic  propeller, and it’s incredibly rare. AE Aquarii and J0240 are the only two  stars that we’ve ever spotted doing this.

The unique alignment of J0240 which allows  the red giant to occasionally eclipse the white dwarf from our point of view. That has allowed scientists to literally see the  blobs of gas as they’re thrown out into space. Each one is a mini-explosion  from the white dwarf’s surface, ejected at about 9.5 million kilometers per hour.

That’s around 1% of the speed of light! The energy for all these ejections comes  from the star’s incredibly fast spin, so with each explosion we expect the  rotation to slow down by a tiny amount. But right now, the discovery  of J0240’s lightning-fast spin and its energetic ejections  is still pretty recent.

So we’ll have to wait a little longer to see  how this strange lawn-sprinkler in the sky   will evolve. Thanks for watching this episode of SciShow Space, and thanks to our patrons, who make it possible  for us to go on the Internet and yell about how cool cataclysmic variables are. We truly couldn’t do this  without your generous support.

I mean, we can and do get  excited about weird space stuff,   but you guys make it possible  for us to share it with everyone. If you want to get involved, you can  get started at patreon.com/scishowspace. [ ♪ OUTRO ♪]  (Our notes included comparing this  rotational speed to the Sun and   wondering what would happen if this  were to happen in our solar system)